We'd like to support general preprocessors with merlin using the new -pp flag but dune's preprocessing is a bit too general to use this flag. Dune allows for any action to act as a preprocessor but it's not that simple to encode as a -pp argument. I see a few workarounds:

• Generate a shell script for a preprocessing action and use it as a -pp argument
• Generate and OCaml script for an action and use that as the -pp argument
• Create a general binary that will interpret dune actions. This action will be executed as the -pp argument with the action serialized appropriately.

Anyone have any other suggestions? Or preferences for any of the options above?